Any plumbers?

[sight-pin]

I hope you don't mind if I add another heating question ...?

From time to time, a central heating system with a combi-boiler makes a loud juddering sound. It only happens when the heating is on, and at random intervals. If left alone, I think that the noise would continue until neighbours banged on the wall to complain, or some part of the system shook itself to pieces! I discovered that if a hot water tap is run for even a second or two, that stops the vibration.

I can't figure out what causes the noise to start or how the separate hot water system interacts with the heating system to stop it.

Any suggestions? (Apart from the obvious 'Consult heating engineer'!)

When you call for hot water the boiler switches over to hot water priority which is probably why the noise stops. Out of interest you haven't fitted every rad/towel rail with TRV's have you? as one (normally the bathroom) is still supposed to have lockshield valves to act as a bypass for the boiler, even though the boiler has an automatic bypass......This is just a thought?

 

[ColinJ]

The central heating circuit on a combi system is isolated from the mains cold and hot water system. I think it would be unlikely that any part of the CH circuit would be the cause of water hammer unless the circulating pump is trying to circulate the CH water into a rapidly closing valve. Circulating pumps usually work at much lower pressures than mains water which usually causes hammer. However, it could be a possibility. One way of testing it would be to see if the hammer still appears even when nobody operates the hot or cold taps in your home.

I live alone so nobody is running taps IN THIS HOUSE when the problem occurs. It only happens now when the heating is on. I am only using a low water temperature to take the chill of the house. The temperature dial is only set to about 15% of max. (It is a simple combi-boiler which does not have a temperature gauge or external thermostat.)

I did get water hammer when my neighbour ran their taps before I reduced the pressure with the stop cock. The water pipe for my neighbour(s?) actually passes through my cellar and a spur off it feeds this house.

Maybe there was still enough pressure for the neighbours to trigger hammer here? I adjusted the stop cock again last night to further reduce the flow into this house. I'll see if the problem happens when I use the heating today.

By shutting the valve you are reducing the pressure and flow rate (speed) of the water and hence reducing the potential for the water hammer to occur. The water hammer is caused by the water stopping as discussed above.

Rather than half close a valve a better approach is to install a pressure reduction valve (PRV). These cost around £30 and are easy to install, should be available from any good plumbers merchant.

A PRV reduces the water pressure under all flow conditions, from no flow to full flow, rather than just high flow and seats in taps, ball cocks, valves, etc. will last longer. Partly shutting the valve to reduce pressure can lead to wire drawing on the valve seat that means when you want it to close off completely it won't.

A PRV does sound like a better solution to that problem. I will get one fitted in the NY.

It could be the boiler is Kettling and by running the hot tap you let cold water into the boiler heat exchanger cooling it down !?

I had to look that up! Interesting ... Hmm, we live in a softwater area so limescale is not a problem and the boiler is only a couple of years old so it should be in good condition. But ... it is only running the hot water that stops the vibration. I can repeatedly cycle the cold water tap and the vibration continues.

Thanks for your suggestions, all of you. I just wanted to get through to January without any major hassle and this problem was starting to bug me.

I am getting an extra radiator fitted in the NY so I will ask the heating engineer to check the system while he is here.

 

[ColinJ]

When you call for hot water the boiler switches over to hot water priority which is probably why the noise stops. Out of interest you haven't fitted every rad/towel rail with TRV's have you? as one (normally the bathroom) is still supposed to have lockshield valves to act as a bypass for the boiler, even though the boiler has an automatic bypass......This is just a thought?

Funnily enough, the bathroom does not have a radiator or heated towel rail in it! It seems like a crazy oversight by whoever fitted the system. The boiler does warm the room slightly but it is obviously one of the most important rooms to heat! That is why I am booking the heating engineer to do some work in January.

 

[User6179]

I had to look that up! Interesting ... Hmm, we live in a softwater area so limescale is not a problem and the boiler is only a couple of years old so it should be in good condition. But ... it is only running the hot water that stops the vibration. I can repeatedly cycle the cold water tap and the vibration continues.

That's what I thought , when you run the hot water you release the pressure and cold water enters the heat exchanger, if your boiler pre heats the hot water so you have instant hot water then you could try changing to eco mode if it has one and see if that works .

 

[ColinJ]

That's what I thought , when you run the hot water you release the pressure and cold water enters the heat exchanger, if your boiler pre heats the hot water so you have instant hot water then you could try changing to eco mode if it has one and see if that works .

It doesn't preheat the water. It is annoying how much water has to be run through before hot water finally emerges. The boiler is the 30 kW version of THIS.

 

[User6179]

It doesn't preheat the water. It is annoying how much water has to be run through before hot water finally emerges. The boiler is the 30 kW version of THIS.

Mine is 30 kw for water as well but I have rubbish pressure ,I run it on eco mode( does not pre heat) for water and it only takes a few seconds for hot water to hit the tap but 20 minutes to fill the bath , counterintuitive but if you run the tap slowly to start with it should give you hot water quicker, I turn mine on full as I only get a piddling 8 litres a minute with my water pressure or less if next door is running water , you wouldn't want to swap high for low pressure !

 

[sight-pin]

Funnily enough, the bathroom does not have a radiator or heated towel rail in it! It seems like a crazy oversight by whoever fitted the system. The boiler does warm the room slightly but it is obviously one of the most important rooms to heat! That is why I am booking the heating engineer to do some work in January.

The reason i asked if all the rad's are fitted with Thermostatic valves is, as the house heats they shut down stopping the flow and if you don't have any without a TRV fitted, that will probably cause the noise as the boilers flow will be reduced especially if the boiler bypass isn't letting by fully.

 

[ColinJ]

Mine is 30 kw for water as well but I have rubbish pressure ,I run it on eco mode( does not pre heat) for water and it only takes a few seconds for hot water to hit the tap but 20 minutes to fill the bath , counterintuitive but if you run the tap slowly to start with it should give you hot water quicker, I turn mine on full as I only get a piddling 8 litres a minute with my water pressure or less if next door is running water , you wouldn't want to swap high for low pressure !

I have discovered that the boiler DOES have a pre-heat mode but you have to turn the water temperature dial beyond maximum to engage it. I only have the dial at about 20% so I had never bothered to look at the far end of the scale! It's not a very 'green' idea having boilers heating water in case it is needed later; that is like going back to immersion heaters and storage radiators!

My attitude generally is to heat the house and water as little as possible, subject to me being reasonably comfortable. My sister heats her house to 22 degrees and will not listen to my argument that that temperature is warmer than a typical summer day in the UK. Her house is cooler than that in summer and she does not heat it then, so why overheat it in the winter! I am happy at about 13 or 14 degrees when wearing my usual warm winter clothes. I used to have my room cooler than that but after recent health problems I decided it would be wise to keep myself a bit warmer ... (Cold blood clots more easily!)

The reason i asked if all the rad's are fitted with Thermostatic valves is, as the house heats they shut down stopping the flow and if you don't have any without a TRV fitted, that will probably cause the noise as the boilers flow will be reduced especially if the boiler bypass isn't letting by fully.

Ah, that's interesting ... I think they ALL have TRVs! I don't have a separate thermostat so I just adjusted the TRVs in my living room to fully on, some elsewhere to low and in a couple of unused rooms they are off.

I will be getting a bathroom radiator in January so I will make sure that doesn't have a TRV.

 

[sight-pin]

I have discovered that the boiler DOES have a pre-heat mode but you have to turn the water temperature dial beyond maximum to engage it. I only have the dial at about 20% so I had never bothered to look at the far end of the scale! It's not a very 'green' idea having boilers heating water in case it is needed later; that is like going back to immersion heaters and storage radiators!

My attitude generally is to heat the house and water as little as possible, subject to me being reasonably comfortable. My sister heats her house to 22 degrees and will not listen to my argument that that temperature is warmer than a typical summer day in the UK. Her house is cooler than that in summer and she does not heat it then, so why overheat it in the winter! I am happy at about 13 or 14 degrees when wearing my usual warm winter clothes. I used to have my room cooler than that but after recent health problems I decided it would be wise to keep myself a bit warmer ... (Cold blood clots more easily!)


Ah, that's interesting ... I think they ALL have TRVs! I don't have a separate thermostat so I just adjusted the TRVs in my living room to fully on, some elsewhere to low and in a couple of unused rooms they are off.

I will be getting a bathroom radiator in January so I will make sure that doesn't have a TRV.

Ok, Other than that... You can remove one of the TRV heads which should/may cure the banging problem, this won't allow that one valve to shut down, just unscrew the knurled alloy knob at the bottom of plastic head to remove. But if your not sure, best wait till the plumber shows up.

 

[slowmotion]

If the hammer originates in the central heating circuit, I suspect that the pump is trying to pump water into a dead end when the last TRV closes. This is known as dead-heading, and it isn't a good idea. The way round it is to have one radiator that never fully turns off , eg no TRV. The alternative is to have an automatic by-pass valve that sends the water into a short loop of pipe when the pressure in the system rises above a pre-set limit. Either option means that the pump will never dead-head.

 

[Globalti]

Much amusement here in the Global house when I read out Colin's description of the mug being blasted from his hand. How many mugs did you break, Colin?

 

[User6179]

I have discovered that the boiler DOES have a pre-heat mode but you have to turn the water temperature dial beyond maximum to engage it. I only have the dial at about 20% so I had never bothered to look at the far end of the scale! It's not a very 'green' idea having boilers heating water in case it is needed later; that is like going back to immersion heaters and storage radiators!

My attitude generally is to heat the house and water as little as possible, subject to me being reasonably comfortable. My sister heats her house to 22 degrees and will not listen to my argument that that temperature is warmer than a typical summer day in the UK. Her house is cooler than that in summer and she does not heat it then, so why overheat it in the winter! I am happy at about 13 or 14 degrees when wearing my usual warm winter clothes. I used to have my room cooler than that but after recent health problems I decided it would be wise to keep myself a bit warmer ... (Cold blood clots more easily!)


Ah, that's interesting ... I think they ALL have TRVs! I don't have a separate thermostat so I just adjusted the TRVs in my living room to fully on, some elsewhere to low and in a couple of unused rooms they are off.

I will be getting a bathroom radiator in January so I will make sure that doesn't have a TRV.

I don't understand the pre heat mode myself as the water heats instantly anyway .

My mother has the heating set at 21 degrees and I realised its because the thermostat control is rubbish , the actual temperature is probably about 25 before the heating cuts out and goes down to about 15 degrees before it comes back on , when it gets cold but digital thermostat still says its over 21 degrees she sticks it in the fridge to get the heating on because she cant work it

 

[ColinJ]

Much amusement here in the Global house when I read out Colin's description of the mug being blasted from his hand. How many mugs did you break, Colin?

Just the one, though it did happen a few more times before I adjusted the stop-cock!

It was annoying me when the original water hammer occurred when I opened and closed taps, but the fact that the neighbours could cause it to happen in my house was really annoying me. I think the man next door must have started doing an early shift because he began getting up at about 04:00. As soon as he turned a tap on the pipes in my house started banging which was waking me up.

I don't understand the pre heat mode myself as the water heats instantly anyway .

I was wondering about that too! I assume that it just keeps part of the heat exchanger warm to save a few seconds warming it up on demand?

The main problem is getting all the cold water out of the pipes to let the hot water through. The taps in the bathroom run hot much quicker than the ones in the kitchen do because they are much closer to the boiler.

 

[User6179]

If the hammer originates in the central heating circuit, I suspect that the pump is trying to pump water into a dead end when the last TRV closes. This is known as dead-heading, and it isn't a good idea. The way round it is to have one radiator that never fully turns off , eg no TRV. The alternative is to have an automatic by-pass valve that sends the water into a short loop of pipe when the pressure in the system rises above a pre-set limit. Either option means that the pump will never dead-head.

But I don't understand how turning the hot water on would help in this situation ?

I was wondering about that too! I assume that it just keeps part of the heat exchanger warm to save a few seconds warming it up on demand?

The main problem is getting all the cold water out of the pipes to let the hot water through. The taps in the bathroom run hot much quicker than the ones in the kitchen do because they are much closer to the boiler.

I think mine holds 2.5 litres of water so no much point pre heating this when I need a bath , might save 10 seconds or so .

Getting the water through is not the problem ,7 metres of 15mm pipe holds about a litre of water and by the sounds of your pressure you will be getting a litre every 5 seconds or so , if you turn on the taps full pelt and you are getting more water than the boiler capacity the water passing through the boiler will take a while before it is hot , my old granny had a Greenstar combi boiler 6 feet from the kitchen sink and water pressure that could cut through stone , if she turned the tap on full it took ages before the water went hot but if she let the water dribble out the tap just enough to turn the boiler on then it only took a few seconds to heat and once it was hot you could turn the tap on more..

 

[Globalti]

I hate combi boilers. Give me a nice big cylinder of hot water any day.

Anyway my DIY solar panel wouldn't work with a combi as it needs to store the solar heated water.